The present invention relates to the determination of the mean wind with respect to the ground during the flight of an aircraft.
Usually, on board an aircraft, for example an aeroplane or else a helicopter, the three components W.sub.N, W.sub.E, W.sub.V, measured in a reference frame related to the ground, of the wind speed with respect to the ground are not known. In fact, airborne instruments exist which deliver the three components S.sub.N, S.sub.E, S.sub.V, measured in a reference frame related to the ground, of the ground speed of the aircraft, as well as the modulus V of the speed of the aircraft with respect to the air mass in which it is moving, also called air speed of the aircraft. Now, the relation which relates W, the speed vector of the wind with respect to the ground, S, the speed vector of the aircraft with respect to the ground and V, the air speed vector of the aircraft is: EQU S=W+V
The result is that the three components of the vector W cannot be determined from the three components of vector S and from the modulus V of vector V alone.
Now, the knowledge of the three components of the wind with respect to the ground is useful on board an aircraft particularly during flight tests, the knowledge of the three components of the wind makes is possible to estimate accurately the performances of the aircraft in the presence of wind. In normal flight, it allows the pilot or certain servomechanisms to act on the control of certain members of the aircraft which are sensitive to the wind and in particular on the firing means carried on board for correcting, as a function of the wind, the firing parameters so that the objectives are reached despite the existence of wind.
An object of the present invention is then to overcome at least partially the drawbacks which appear for aircraft on board of which the three components of the wind speed with respect to the ground are not known.
For this, it has first of all as object a method for determining the three components W.sub.N, W.sub.E, W.sub.V, in an Earth reference frame, of the speed with respect to the ground of the mean wind during a flight period of an aircraft, for controlling equipment of said aircraft which is sensitive to the wind, in which:
at each time of rank i of a succession of times spread out over said period, the value V.sub.i of the modulus of the speed of the aircraft with respect to the air mass in which it moves and the values S.sub.Ni, S.sub.Ei, S.sub.Vi of the three components, in said Earth reference frame, of the ground speed of said aircraft are measured,
said measured values are stored and
using the method of least squares, a system of equations with three unknowns W.sub.N, W.sub.E, W.sub.V is solved, in which system the current equation is: EQU 2(S.sub.Ni -S.sub.NR)W.sub.N +2(S.sub.Ei -S.sub.ER)W.sub.E +2(S.sub.Vi -S.sub.VR) W.sub.V =S.sub.Ni.sup.2 -S.sub.NR.sup.2 +S.sub.Ei.sup.2 -S.sub.ER.sup.2 +S.sub.Vi.sup.2 -S.sub.VR.sup.2 +V.sub.R.sup.2 -V.sub.i.sup.2
V.sub.R, S.sub.NR, S.sub.ER and S.sub.VR being values stored before the time of rank i, of said modulus and of said three components of the ground speed of said aircraft, respectively.
It will be noted that the method of the invention does not propose determining, at each time of rank i, the three components W.sub.Ni, W.sub.Ei, W.sub.Vi from the knowledge of the three components S.sub.Ni, S.sub.Ei, S.sub.Vi and of the modulus V.sub.i alone. It is obvious that such determination is impossible. However, the Applicant having observed that generally the wind remains substantially constant in the Earth reference frame during a flight, he has perfected the method of the invention which makes possible the determination of the three components of the means wind during this flight, which components already form useful data.
In the method of the invention, and as will be better understood hereafter, the insufficiency of the number of independent measurements at each measuring time is compensated for by the plurality of measuring times. This characteristic, associated with a judicious equation arrangement makes it possible, assuming that the wind remains substantially the same, to determine the three unknown components.
The present invention also has as object a method of determining the three components W.sub.N, W.sub.E, W.sub.V, in an Earth reference frame, of the speed with respect to the ground of the mean wind during a flight period of an aircraft, for controlling the equipment of said aircraft sensitive to the wind, in which:
at each time of rank i of a succession of times spread out over said period, the value V.sub.i of the modulus of the speed of the aircraft with respect to the air mass in which it moves, the values S.sub.Ni, S.sub.Ei, S.sub.Vi of the three components, in said Earth reference frame, of the ground speed of said aircraft, and the value .theta..sub.i of the pitch angle are measured,
said measured values are stored,
the vertical component W.sub.V is computed from the formula: ##EQU1##
and using the method of least squares, the system of equations is solved in which the two unknowns are the two horizontal components W.sub.N and W.sub.E, in which system the current equation is: EQU 2(S.sub.Ni -S.sub.NR)W.sub.N +2(S.sub.Ei -S.sub.ER)W.sub.E =S.sub.Ni.sup.2 -S.sub.NR.sup.2 +S.sub.Ei.sup.2 -S.sub.ER.sup.2 +V.sub.R.sup.2 cos .sup.2 .theta..sub.R -V.sub.i.sup.2 cos .sup.2 .theta..sub.i
V.sub.R, S.sub.NR, S.sub.ER and .theta..sub.R being values, stored before the time of rank i, of said modulus, of said two horizontal components of the ground speed of said aircraft and of said pitch angle, respectively.
In the case where the vertical component of the wind is small, this method makes rapid determination possible.
In a first implementation of the method of the invention said succession of times spread out over said period comprises in all n times, n being at least equal to three, said values stored before the time of rank i are those measured at any time of rank j less than i, and a system of n (n-1)/2 equations is solved.
This implementation makes it possible to obtain an accurate result for it is established from a large number of equations.
In a second implementation of the method of the invention, said values stored before the time of rank i are averages of a plurality of values measured at times of rank j, less than i, and a system of (i-1) equations is solved in real time.
This implementation is well adapted to real time determination for the computing time is relatively reduced.
The invention also has as object a device for implementing the above method, for determining the three components W.sub.N, W.sub.E, W.sub.V, in an Earth reference frame, of the speed with respect to the ground of the mean wind during the flight of an aircraft, for controlling equipment of said aircraft which is sensitive to the wind, comprising:
means for measuring, at each time of rank i of a succession of times spread out over said period, the value V.sub.i of the modulus of the speed of the aircraft with respect to the air mass in which it moves and the values S.sub.Ni, S.sub.Ei, S.sub.Vi of the three components, in said Earth reference frame, of the ground speed of said aircraft,
means for storing said measured values and
means for solving, using the method of least squares, a system of equations with three unknowns W.sub.N W.sub.E W.sub.V, in which system the current equation is: EQU 2(S.sub.Ni -S.sub.NR)W.sub.N +2(S.sub.Ei -S.sub.ER)W.sub.E +2(S.sub.Vi -S.sub.VR)W.sub.V =S.sub.Ni.sup.2 -S.sub.NR.sup.2 +S.sub.Ei.sup.2 -S.sub.ER.sup.2 +S.sub.Vi.sup.2 -S.sub.VR.sup.2 +V.sub.R.sup.2 -V.sub.i.sup.2
V.sub.R, S.sub.NR, S.sub.ER and S.sub.VR being values, stored before the time of rank i in said storage means, of said modulus and of said three components of the ground speed of said aircraft, respectively.